Chemical Characterization of the Volatiles of Leaves and Flowers from Cultivated Malva sylvestris var. mauritiana and their Antimicrobial Activity Against the Aetiological Agents of the European and American Foulbrood of Honeybees (Apis mellifera)

Abstract

The composition of the volatile fraction of Malva sylvestris var. mauritiana (L.) Boiss. (Malvaceae) was investigated. This plant species was cultivated in the southeastern Alps as an ingredient for herbal teas and infusions. Flowers and leaves were collected at the end of the summer season and separately steam- distilled to obtain two volatile oils, the yields of which were 0.019% for leaves and 0.012% for flowers. After GC-FID and GC-MS analyses, the two oils -revealed differences in the nature and especially in the proportion of their components, which were aldehydes, alcohols, phenolics, esters, hydrocarbons and acids. Eugenol was the single most abundant compound in the leaves, totalling 46.7% of the total oil, followed by phytol with 34.4%. Flowers showed a predominance of hydrocarbons, among which the anteiso branched-chain saturated hydrocarbon, 3-methyl tricosane, was the most abundant compound, accounting for 14.9% of the total volatiles. Eugenol ranked second with 10.3%, followed by the two linear-chain saturated hydrocarbons pentacosane and tricosane forming 8.2 and 7.7% of the total oil, respectively. The occurrence and the relative abundance of compounds from various chemical classes such as phenolics, hydrocarbons and aromatic aldehydes and alcohols are discussed, together with some of their ecological implications. The obtained volatile oils were than tested against two major honeybee (Apis mellifera) pathogens, namely Paenibacillus larvae and Melissococcus plutonius, the causative agents of the American and the European foulbrood, respectively.